Whether certain foods worsen acne has long been the subject of debate. At the moment, there are a few foods that have been shown in some scientific studies to worsen acne. Studies have shown that excessive consumption of milk, especially skim milk, can worsen acne, perhaps by increasing sebum production. A "high-glycemic diet" that is high in sugary, processed foods may also contribute to acne.
Some dermatologists think that in rare cases, consuming large amounts of shellfish or kelp that have iodine in them may cause a type of acne. This is based on a few case reports from the 1970s and on the observation that medications that contain large amounts of iodine can cause an acne-like eruption.
There is no convincing scientific evidence that eating chocolate or greasy foods causes or worsens acne; this is currently thought to be a myth. In most cases, acne is not caused by one's diet but rather by such factors as genetics and hormones.
Eating a healthy, balanced diet that is low in sugary, processed foods and contains plenty of fruits and vegetables is a sensible approach to take for your health. Some scientific evidence suggests that this may also be beneficial for your skin.